scoped_resource.hpp

/*
    scoped_resource
 
    BSD 3-Clause License
 
    Copyright (c) 2026, Abdulkareem Siddiq
    All rights reserved.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
 
    1. Redistributions of source code must retain the above copyright notice,
    this list of conditions and the following disclaimer.
 
    2. Redistributions in binary form must reproduce the above copyright notice,
        this list of conditions and the following disclaimer in the documentation
        and/or other materials provided with the distribution.
 
    3. Neither the name of the copyright holder nor the names of its
        contributors may be used to endorse or promote products derived from
        this software without specific prior written permission.
 
    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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    POSSIBILITY OF SUCH DAMAGE.
 */
 
#pragma once
#ifndef SCOPED_RESOURCE_HPP
#define SCOPED_RESOURCE_HPP
 
#include <atomic>
#include <concepts>
#include <cstdint>
#include <format>
#include <functional>
#include <stdexcept>
#include <type_traits>
 
#include "common.hpp"
 
namespace siddiqsoft::arrp
{
    template <typename T>
    concept NonNumericMoveConstructible = std::move_constructible<T> && !std::is_arithmetic_v<T>;

    template <typename T>
        requires NonNumericMoveConstructible<T>
    class scoped_resource
    {
        // Allow resource_pool to access protected members
        template <typename U, typename SRT, uint8_t IC>
            requires((IC <= resource_pool_limits::MaxCapacity)) && NonNumericMoveConstructible<U> &&
                    std::derived_from<SRT, scoped_resource<U>>
        friend class resource_pool;
 
    protected:
        T m_rsrc {};

        std::function<void(T&&)> m_putback_callback {};

        bool m_is_valid {false};
 
    public:
        scoped_resource() = delete;

        explicit scoped_resource(T&& src, std::function<void(T&&)>&& f = {})
            : m_rsrc(std::move(src))
            , m_putback_callback(std::move(f))
            , m_is_valid(true)
        {
        }

        explicit scoped_resource(const T&) = delete;

        scoped_resource(scoped_resource&& src) noexcept
            : m_rsrc(std::move(src.m_rsrc))
            , m_putback_callback(std::move(src.m_putback_callback))
            , m_is_valid(src.m_is_valid)
        {
            // Reset to ensure that the source does not double return!
            src.m_putback_callback = {};
            src.m_is_valid         = false;
        }

        scoped_resource& operator=(scoped_resource&& src) noexcept
        {
            if (this != &src) {
                // Return current resource if valid
                if (m_is_valid && m_putback_callback) {
                    m_putback_callback(std::move(m_rsrc));
                }
 
                // Move from src
                m_rsrc             = std::move(src.m_rsrc);
                m_putback_callback = std::move(src.m_putback_callback);
                m_is_valid         = src.m_is_valid;
 
                // Reset src
                src.m_putback_callback = {};
                src.m_is_valid         = false;
            }
            return *this;
        }

        scoped_resource& operator=(T&& src)
        {
            m_rsrc     = std::move(src);
            m_is_valid = true;
            return *this;
        }

        scoped_resource& operator=(const scoped_resource&) = delete;

        auto operator*() -> T& { return m_rsrc; }
 
             operator T&() { return m_rsrc; }

        ~scoped_resource()
        {
            // Only return resource if it's valid and callback exists
            // This prevents returning uninitialized or moved-out resources to the pool
            if (m_is_valid && m_putback_callback) {
                m_putback_callback(std::move(m_rsrc));
                m_is_valid         = false;
                m_putback_callback = {};
            }
        }

        void invalidate() { m_is_valid = false; }
 
#if defined(NLOHMANN_JSON_VERSION_MAJOR)
        nlohmann::json to_json() const
        {
            return {{"_typver", "siddiqsoft.arrp.scoped_resource/0.0.0"}, {"capacity", m_is_valid}, {"value", m_rsrc}};
        }
#endif
    };
} // namespace siddiqsoft::arrp
 
#endif